<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        #outBox{
            height: 100px;
            list-style-type: none;
        }
        #outBox li{
            width: 0;
            padding: 30px;

        }
        .inBox1{
            float: left;
            background: rgba(0,0,0,1);
        }
        .inBox2{
            float: left;
            background: rgba(0,0,0,0.8);
        }
        .inBox3{
            clear: left;
            background: rgba(0,0,0,0.6);
        }
        .inBox4{
            float: left;
            background: rgba(0,0,0,0.4);

        }
        .inBox5{
            float: left;
            background: rgba(0,0,0,0.2);
        }
    </style>
</head>
<body>
    <ul id="outBox">
       <li class="inBox1"></li>
       <li class="inBox2"></li>
       <li class="inBox3"></li>
       <li class="inBox4"></li>
       <li class="inBox5"></li>
    </ul>
</body>
</html>